#JavaScript, Z (90) bytes

for(i=65,b=66;i<91;++i,b=b<90?++b:65)console.log(Array(14).join(String.fromCharCode(i,b))) 

To learn:

var start = 65, end = 90; for (var i = start, b = i+1; i <= end; ++i) { var chars = String.fromCharCode(i, b); /* repeat chars 14 times */ console.log(Array(14).join(chars)); } 

JavaScript, Z (90) bytes

for(i=65,b=66;i<91;++i,b=b<90?++b:65)console.log(Array(14).join(String.fromCharCode(i,b))) 

To learn:

var start = 65, end = 90; for (var i = start, b = i+1; i <= end; ++i) { var chars = String.fromCharCode(i, b); /* repeat chars 14 times */ console.log(Array(14).join(chars)); } 

#JavaScript, Z (90) bytes

for(i=65,b=66;i<91;i++,b=b<90?++b:65)console.log(Array(14).join(String.fromCharCode(i,b))) 

#JavaScript, Z (90) bytes

for(i=65,b=66;i<91;++i,b=b<90?++b:65)console.log(Array(14).join(String.fromCharCode(i,b))) 

To learn:

var start = 65, end = 90; for (var i = start, b = i+1; i <= end; ++i) { var chars = String.fromCharCode(i, b); /* repeat chars 14 times */ console.log(Array(14).join(chars)); } 

#JavaScript, Z bytes

for(i=65,b=66;i<91;i++,b=b<90?++b:65)console.log(Array(14).join(String.fromCharCode(i,b))) 

Using bad pratices, but shortest.

#JavaScript, Z (90) bytes

for(i=65,b=66;i<91;i++,b=b<90?++b:65)console.log(Array(14).join(String.fromCharCode(i,b)))